Refractory metal boat for heat treating coils

ABSTRACT

A boat for heat treating refractory wire coils comprises a molybdenum enclosure having a corrugated molybdenum sheet attached therein to form an integral compartmentalized boat. The corrugated sheet is locked to the boat in such a manner as to permit thermal expansion thereof independently of the boat. Each curved hollow of the corrugated sheet can contain a plurality of coils in such a manner as to prevent distortion thereof during heat treating.

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nite States atet ns1 3,638,930 Hart, Jr. [45] Feb. l, 1972 [54] REFRACTORY'METAL BOAT FOR Primary Examiner-John J. Camby HEAT TREATING COILS Attorney-Norman J. OMalley and James Theodosopoulos [72] Inventor: Halver Allen Hart, Jr., Waldoboro, Maine [57] ABSTRACT [73] Assignee: Sylvania Electric Products Inc- A boat for heat treating refractory wire coils comprises a [22] Filed: APL 24 1970 molybdenum enclosure having a corrugated molybdenum sheet attached therein to form an integral compartmcntalized [21] APPL NO- 31,559 boat. The corrugated sheet is locked to the boat in such a manner as to permit thermal expansion thereof` independently [521 u s. ci. 263/47 R, 263/49 R ofthe boa [5 ll lm Cl v F27b 21/04, F27d 5/00 Each curved hollow of the corrugated sheet can contain a plu- [58] Field 0f Search --263/47 R, 47 A, 48 R, 49 R, rality of coils in such a manner as to prevent distortion thereof 263/49 B during heat treating. [56] References Cited 5 Claims, 3 Drawing Figures UNITED STATES PATENTS 2,026,311 12/1935 Harris n263/49 PATENTEU FEW H97? HALvER ALLEN HART JR mveNToR l, ,lvA ,l ll i BY ATTORNEY BACKGROUND OF THE INVENTION l. Field of the Invention This invention relates to the field of refractory metal boats which are used in heat treating refractory wire coils such as, for example, incandescent lamp filaments. It especially relates to such boat as are passed through a high-temperature furnace to effect heat treating ofthe coils.

2. Description ofthe Prior Art In the manufacture of some helical coils, such as coiled coil incandescent lamp filaments, a continuous length of tungsten wire is primary coiled on a continuous length of a molybdenum wire mandrel and taken up on a suitable spool. The wire is then annealed by passing it through a high-temperature furnace.

The annealed coiling is then secondary coiled and cut into specific lengths to form filaments of predetermined characteristics. These filaments comprise straight lengths of coiled coiling and often have ends or legs at each end which extend axially of the body and which comprise short sections of the primary coiling. These ends or legs are suitable for mounting the finished filament in an incandescent lamp mount by welding or crimping the legs to lead-in wires.

It is necessary that the coiled coils be heat treated or sintered at a high temperature in order that the filaments be properly set and retain their shape throughout subsequent manufacturing processes and especially throughout the step of mandrel removal, where the coils are immersed in acid to dissolve the molybdenum mandrel. 1

In the past, the coiled coil filaments were randomly collected in a container at the secondary coiling machine and subsequently were individually removed from the container and carefully placed in an elongated, rectangular boat for heat treating.

Later, as the secondary coiling operation increased in production rate and became more mechanized, the coiled coils were automatically deposited from the coiling machine onto an unenclosed convoluted molybdenum sheet metal insert which, in turn, was placed, when full, into a separate boat for sintering. A disadvantage to this method of processing coils involved coils falling or sliding out of the insert during the transfer thereof to the boat. A result of this was improper coil alignment during sintering and rejection coils for nonuniform straightness.

In addition, individual handling of the relatively brittle inserts often resulted in a high rate of breakage. And the fact that the inserts were not locked within the boats during the sintering operation often resulted in such distortion of the inserts as to render them unusable. Also, in order to insure that the inserts would continually fit into the sintering boat throughout their useful life, there was necessarily a large tolerance therebetween, with the result that coils could fall or become lodged in the space therebetween.

SUMMARY OF THE INVENTION A boat in accordance with this invention comprises a molybdenum enclosure having a corrugated molybdenum sheet therewithin; each curved hollow of the corrugated sheet capable of serving as a container for a plurality of helical coils. The sides of the boat complete the container for each hollow, the depth ofeach hollow being less than the height ofthe boat.

The corrugated sheet is attached to the enclosure in such a manner as to be locked in place therein, however, being rigidly attached thereto. Thus, although the enclosure and corrugated sheet comprise an integral unit, the corrugated sheet is free to thermally expand and contract independently of the enclosure, the reason therefor being to minimize strains and, consequently, distortion and/or fracture of the corrugated sheet.

BRIEF DESCRIPTION OF THE DRAWING FIG. 1 is an exploded view of a boat in accordance with this invention.

FIG. 2 is a perspective view of the same boat and FIG. 3 is an elevational cross-sectional view along line 3 3 of FIG. 2.

DESCRIPTION OF THE PREFERRED EMBODIMENT As shown in the drawings, boat l comprises a corrugated sheet 2 locked within an enclosure 3. Corrugated sheet 2 and enclosure 3 are both fabricated from ductile molybdenum sheet metal capable of being worked at room temperature and able to withstand sintering temperatures in the order of l,600 to l,800 C. without melting.

ln one specific example, enclosure 3 was fabricated from two elongated precut strips of 66-mil thick molybdenum that overlapped each other at the ends and were bent under at their lower edge to form the bottom of enclosure 3. The overlapping ends were fastened together by means of molybdenum dowels 4 extending across enclosure 3, the ends of dowels 4 being peened. The lower ends of enclosure 3 were curved to provide ease of passage of the boats through high-temperature A furnaces. ln this example, enclosure 3 was l0 inches long by l inch high by 1 inch wide.

Corrugated sheet 2 is shaped so as to fit substantially snugly within enclosure 3 in order that there be no cracks or openings therebetween in which coils could become lodged. Also corrugated sheet 2 is contoured so that the volume contained within the hollows thereof is considerably larger than the volume within the ridges. The purpose of this is to provide efficient usage of the total space within boat l for the containment of coils, since coils can be contained only in the hollows of the corrugations. In the above example, the radius of curvature of a typical hollow, identified as element 5 in FIG. 3, was five-sixteenths inch; in contrast, the radius of curvature of a typical ridge, identified as element 6 in FIG. 3, was only five sixtyfourths inch.

Corrugated sheet 2 was locked to enclosure 3 by means of molybdenum dowels 7 extending across enclosure 3 and through the sides thereof. As in the case of dowels 4, the ends ofdowels 7 were also peened to secure them to enclosure 3.

Dowels 7 were arranged so as to pass just above the lowest point ofa hollow 5 or just below the highest point of a ridge 6 at one or more places throughout the boat. By positioning a dowel 7 in each hollow S at the ends of the boat, corrugated sheet 2 was effectively locked in place and could not be lifted out of the boat. Positioning a dowel 7 through a ridge 6 at about the center of the boat aided in preventing sagging of corrugated strip throughout the life of the boat. The diameter of the latter dowel 7 was so related to the radius of curvature of ridge 6 as to substantially prevent longitudinal movement of corrugated sheet 2 relative to enclosure 3. ln the example mentioned, dowel 7 had -a diameter of one-eighth inch in relation to the 5/64-inch radius of curvature of ridge 6.

The ends of corrugated sheet 2 consisted of short straight portions slanted upward so as to make contact with the upper edge ofthe ends of enclosure 3, the purpose thereof being to facilitate loading of the boat as coils were deposited therein from a coiling machine.

In operation, boat l was connected to a coiling machine in such a manner that finished coils from the machine rolled or slid into the boat with their axes parallel with the axes of hollows 5. Thus the coils piled up uniformly within each hollow 5, the curved sides of hollow 5 aiding in the proper alignment of the coils. As each compartment of the boat was filled, the boat was automatically advanced by the coiling machine drive to deposit coils in the next compartment.

Ridges 6 were only about three-quarters of the height of boat 1 in order to permit a molybdenum cover to be placed on top of the coils within the boat. Such a cover can be used if it is desired to shield the uppermost coils from direct radiated heat in the furnace in order to more nearly equalize the heating rate of all the coils within the boat.

l claim:

l. A refractory metal boat for the heat treating of straight helical coils comprising a molybdenum sheet metal enclosure and a corrugated molybdenum sheet having curved hollows and ridges disposed within said enclosure and locked thereto,

each of said hollows comprising a container for a plurality of 5 said coils and wherein said corrugated sheet is locked within said enclosure by means of refractory metal dowels extending across and through the sides ofsaid enclosure.

2. The boat ofclaim l wherein said enclosure comprises two elongated molybdenum strips folded over one another at the ends thereof and fastened together by means of refractory 

1. A refractory metal boat for the heat treating of straight helical coils comprising a molybdenum sheet metal enclosure and a corrugated molybdenum sheet having curved hollows and ridges disposed within said enclosure and locked thereto, each of said hollows comprising a container for a plurality of said coils and wherein said corrugated sheet is locked within said enclosure by means of refractory metal dowels extending across and through the sides of said enclosure.
 2. The boat of claim 1 wherein said enclosure comprises two elongated molybdenum strips folded over one another at the ends thereof and fastened together by means of refractory metal dowels.
 3. The boat of claim 1 wherein the radius of curvature of said hollows is greater than the radius of curvature of said ridges.
 4. The boat of claim 1 wherein said corrugated sheet fits substantially snugly within said enclosure.
 5. The boat of claim 1 wherein the ends of said corrugated sheet slant upwards and contact the upper edge of the ends of said enclosure. 